Fix wrong requirements file path

Author: Surgo

tox.ini

@@ -19,7 +19,7 @@ deps =
     dj110: Django>=1.10,<1.11
     dj111: Django>=1.11,<2.0
     djdev: https://github.com/django/django/archive/master.tar.gz
-    -r requirements.txt
+    -r{toxinidir}/requirements.txt
 setenv =
     PYTHONPATH = {toxinidir}
 commands = coverage run --source=django_elastipymemcache -m nose